Although the role of core circadian gene
cryptochrome 2 (CRY2) in breast
tumorigenesis has been demonstrated, the correlations of CRY2 with clinical parameters in
breast cancer patients and its involvement in epigenetic processes such as DNA methylation remain relatively unexplored. In the current study, we first queried the Oncomine database and the Gene Expression-Based Outcome for
Breast Cancer Online (GOBO) database to identify associations between CRY2 expression levels and clinical parameters in
breast cancer patients. We then silenced CRY2 in vitro and performed a genome-wide methylation array to determine the epigenetic impact of CRY2 silencing. The Ingenuity Pathway Analysis software was used to further explore the genes exhibiting altered methylation identified using the array. We found that CRY2 was frequently down-regulated in
breast cancer tissue compared to adjacent normal tissue or breast tissue from healthy controls. Lower CRY2 expression was associated with
estrogen receptor (ER)-negativity (P < 0.0001), higher
tumor grade (P < 0.0001), and shorter overall survival time in
breast cancer patients (HR = 1.44, 95 % confidence interval (CI) 1.09-1.91). Genome-wide methylation analysis showed that a total of 515 CpG sites were hypermethylated following CRY2 knockdown, while 730 sites were hypomethylated. The pathway analysis revealed several
cancer-relevant networks with genes exhibiting significantly altered methylation following CRY2 silencing. These findings suggest that the core circadian gene CRY2 is associated with
breast cancer progression and prognosis, and that knockdown of CRY2 causes the epigenetic dysregulation of genes involved in
cancer-relevant pathways, which provide further evidence supporting a role of the circadian system in breast
tumorigenesis.